Electric discharge tube



June 16, 1936. J JONKER 2,044,613

ELECTRIC DI S CHARGE TUBE Filed Feb. 1, 1954 IHHIHHHHHIHHMHHIHHHHHH lrnrlnnlllrlllllllll iNVENTOR ATQ'ORNEY Patented June 16, 1936 UNITED STATES ELECTRIC DISCHARGE TUBE Johan Lodewyk Hendrik Jonker, Eindhoven, Netherlands, assignor to Radio Corporation of America, a corporation of Delaware Application February 1, 1934, Serial No. 709,275 In Germany February 6, 1933 2 Claims.

This invention relates to an electric discharge tube having a cathode, preferably indirectly heated, and one or more grids.

It is known to make grids for electric discharge tubes of a wire which is wound on two or more supports so that a number of parallel wire parts is obtained. When using such grids in electric discharge tubes, for instance for generating, receiving or amplifying electric oscillations, the drawback has often been encountered that due to the heat emitted or generated by the cathode, the grid is heated to such a temperature that electron emission occurs from the grid.

Various means for avoiding or reducing said electron emission from the grid have already been proposed. It is known, for instance, to coat the grid with a substance which does not emit electrons or only to an extremely low extent. Furthermore, it is known to make the anode of an electric discharge tube of metallic gauze or wire by which the heating of the grid to an undue temperature by anode reflection is avoided.

It has been found that when narrowly wound grids with very thin wires are used, the grid emission may constitute a serious drawback for the right working of the tube, and I have succeeded completely to avoid this drawback in a very simple manner by using the discharge tube according to the invention.

The novel tube comprises one or more grids consisting of a number of parallel wire posts having a thickness of less than 100 (100 microns) and a cathode, preferably indirectly heated, whose carrier of the emissive layer consists of a material having a smaller radiation power than nickel.

By this arrangement, although the cathode has the same properties, a smaller quantity of energy in the form of heat is radiated from the cathode into the tube, owing to which the material of the grid is heated to a materially lower temperature than is the case with known tubes, so that substantially no primary grid emission can occur. As a material for the carrier body of the emissive layer of the cathode preferably copper is used. However, it is also possible to use for this purpose gold, silver or alloys of these metals.

It has turned out to be very advantageous to make the thickness of the emissive layer less than 0.05 mm. In fact, the advantage is obtained in this case that the emissive layer plays practically no part as regards its radiation. In this case only the radiation of the substratum is of importance and this radiation is materially smaller than when using a cathode with which the emissive layer is applied on to nickel.

It has been found to be advantageous to form the grids of grid wires having a thickness of 50 (50 microns) or less, the shadow ratio being at least 1 to 4. By shadow ratio is meant the ratio between the surface of the grid material projected on a plane parallel with the grid, and between the surface of the apertures in the grid which are also projected on such a plane.

The invention will be more clearly understood by reference to the accompanying drawing representing, by way of example, one form of construction thereof.

In the figure the wall of the tube is denoted by i, which wall is provided with a pinch 2 through which are taken out the supply conductors 3, i and 5 of the cathode, the supply conductor 5 of the grid and the supply conductor l of the anode.

The indirectly heated cathode 8 is constituted by a heating body 9 which is provided within a cathode tube ID, with the interposition of an insulating layer, if desired, which tube is preferably made of copper. The particular cathode construction is more fully described and claimed in an application by Dirk Lely, Jr., et al., filed December 7, 1933, Ser. No. 701,285, and assigned to the same assignee as the present application. The cathode is surrounded by a grid ii consisting of very thin wires which are wound on a few supporting posts I2, only two such posts being shown. The grid is provided on the outer side with particular cooling members l3. The grid is surrounded by a cylindrical anode it, which is mounted on the pinch by means of two supports l5. One of these supporting members serves at the same time for the supply of current to the anode.

It will be appreciated that the invention is not limited to this form of construction, but that Various other forms of construction may readily fall under the scope thereof.

What I claim is:

1. An electron discharge tube comprising a cathode having a base of lower heat radiation than nickel and an emissive layer applied to said base, a grid electrode surrounding the cathode, the grid electrode having turns of wire of a thickness of the order of 50 microns whereby it is incapable of absorbing sufficient heat from the low heat radiating cathode to permit it to emit electrons, and an additional electrode surrounding the grid.

2. An electron discharge tube comprising a cathode having a copper base which has a lower heat radiation than nickel and an emissive layer applied to said copper base, a grid electrode surrounding the cathode, the grid electrode having turns of Wire of a thickness of the order of 50 microns and having a shadow ratio of approximately 1 to 4 whereby it is incapable of absorbing suflicient heat from the low heat radiating cathode to permit it to emit electrons, and an additional electrode surrounding the grid.

JOHAN LODEWYK HENDRIK JONKER. 

